Onion virus appears early this year

Symptoms of iris yellow spot virus in onions have appeared earlier than normal in the Treasure Valley area this year and growers are being encouraged to be extra-vigilant in their thrips management programs.

NYSSA, Ore. — Symptoms of iris yellow spot virus have appeared on onions earlier than normal this year and growers in this area are being urged to be vigilant in their thrips control programs.

The virus, which weakens the plant and reduces onion production, was detected in a commercial onion bulb field in Malheur County, Ore., this week, said Stuart Reitz, an Oregon State University cropping systems extension agent in Ontario.

It was confirmed by diagnostic tests and Reitz said the advanced symptoms present on some of the plants suggests the infection had been present for several weeks.

The Treasure Valley area of southwestern Idaho and eastern Oregon produces about 25 percent of the nation’s fresh bulb onion supply.

An unusually hot summer last year led to a significant increase in onion thrips, which are a vector for the virus. The virus appeared about a week earlier this year than during 2013 and at least a month earlier than the historical norm, Reitz said.

He said growers should ensure they get on top of the issue early this year and pay special attention to fields near over-wintering onions, since they can act as a bridge for onion thrips and the virus.

“Growers really need to pay attention to what’s going on and focus on their thrips management program and spraying insecticides as needed,” Reitz said. “Last year was a bumper crop for thrips and nobody wants to go down that road again.”

Stressed onion plants are particularly susceptible to the virus, he said, and farmers should minimize stress as much as possible by ensuring their fields maintain adequate fertility and soil moisture levels. This helps reduce the severity of the symptoms.

Nyssa area farmer Paul Skeen started spraying his onion crop earlier than normal this year and plans to spray every 10 days instead of every 14 days, which he has done in the past.

“We’re trying to keep the thrips population down so we can keep that virus down,” said Skeen, president of the Malheur County Onion Growers Association. “All indications are it’s supposed to be hotter than normal and we’re trying to stay on top of it.”

“That’s the good approach, to not let things get out of hand,” Reitz said. “By the time you see it in abundance, you’re already behind the 8-ball.”

Nyssa grower Reid Saito said last year’s particularly hot summer caused the virus to be a major problem in some areas of the valley.

“There was some degree of the virus pressure everywhere,” he said. “It was a pretty bad year for the virus. I think growers are trying to stay on top of it (this year.)”